I. Technical Field
The present invention relates to a fixed constant velocity universal joint disposed between two axes on a driving side and a driven side in a power transmission system of automobiles and various industrial machineries, the fixed constant velocity universal joint allowing only angular displacement. The present invention achieves improvements in torsional fatigue strength and quasi-static torsional strength at a high operating angle.
II. Description of the Related Art
A fixed constant velocity universal joint is generally used in an axle connecting section of a drive shaft and a shaft bend connecting section of a steering shaft in an automobile. A Rzeppa-type constant velocity universal joint and an undercut-free type (referred to, hereinafter, as a UJ-type) constant velocity universal joint are conventionally known as the fixed constant velocity universal joint described above. On the other hand, when a wheel base is extended in view of improvements in ride comfort and collision safety of the automobile, the vehicle rotation radius increases. To reduce the vehicle rotation radius, a steering angle of front wheels is required to be increased by the angle of the fixed constant velocity universal joint being increased.
The Rzeppa-type constant velocity universal joint that is a fixed constant velocity universal joint includes an outer member, an inner member, balls, and a cage. A plurality of curved ball grooves are formed evenly spaced on an inner spherical surface of the outer member. The same number of curved ball grooves are formed on an outer spherical surface of the inner member. A center of curvature of the outer member ball grooves and a center of curvature of the inner member ball grooves are offset from a center O of the joint by equal distances to the right and left. A ball is incorporated between an outer member ball groove and an inner member ball groove, and the cage is incorporated between the outer member and the inner member. The cage has spherical surfaces on the inside and outside, the spherical surfaces being in contact with and guided by the inner spherical surface of the outer member and the outer spherical surface of the inner member. The cage also has windows that house the balls and are evenly spaced in a circumferential direction.
The UJ-type fixed constant velocity universal joint has been invented to achieve a higher operating angle than the Rzeppa-type constant velocity universal joint. As shown in FIG. 9, in a ball center trajectory (C3 center) of a ball groove 114 on an outer member 110, among arcs of a meridional line of the above-described Rzeppa-type, a portion closer to an opening side of the outer member 110 than a cross-section perpendicular to an axis passing through a ball groove center (C3) of the outer member 110 is a straight line parallel to a joint axis C L. C2 is an inner spherical surface center of the outer member 10.
FIGS. 5(A) and (B) show the outer member 110 for a constant velocity universal joint having eight balls. 112 indicates an inner spherical surface. 114 indicates a ball groove. 116a indicates a chamfer. 116b indicates a cylindrical section. α0 indicates a spherical surface angle. D0 indicates an axial direction distance from the center of the outer member 110 to a starting position of the cylindrical section 16b. When the cage 120 in FIG. 6 is incorporated into the outer member 110, as shown in FIG. 7 and FIG. 8, the cage 120 is inserted from an axial direction of the outer member 110 in a state in which an axial line of the cage 120 is tilted by 90 degrees to an outer member axial line (refer to FIG. 12 in Japanese Patent Laid-open Publication No. Heisei 6-193645, FIG. 5 in Japanese Utility Model Laid-open Publication No. Heisei 5-45253, and FIG. 5 in Japanese Patent Laid-open Publication No. Heisei 9-177814). As another method, the axial lines of the cage 120 and the outer member 110 can be on a same axis, and the cage 120 can be inserted from the axial direction of the outer member 110 (refer to FIG. 5 in Japanese Utility Model Laid-open Publication No. Showa 54-93850).
In the former insertion method, more specifically, an inner member (not shown) is tilted by 90 degrees to the cage 120. After the inner member is inserted into the cage 120 in this state, both components are relatively rotated by 90 degrees in a direction in which an axial center of the cage 120 and an axial center of the inner member are aligned, and the inner member is incorporated into the cage 120. Next, the inner member with the cage 120 and the outer member 110 are relatively tilted to 90 degrees as shown in FIG. 7 and FIG. 8. After the inner member with the cage 120 is inserted into the outer member 110, both components are tilted by 90 degrees in a direction in which axial centers of the outer member 110 and the inner member are aligned, and the inner member with the cage is incorporated into the outer member 110.